When dentists are finished preparing a cavity in a tooth to receive a restorative material, they almost always line the cavity with a material called a "cavity liner" or "cavity varnish." That material is supposed to decrease the permeability of the dentin to any of the potentially injurious materials placed in the cavity during its restoration or to any microbial products from the oral fluids that might gain access to the inner parts of the cavity in the event that the restorative material might permit microleakage around its margins with the tooth. The most popular cavity varnishes contain organic "gums" dissolved in organic solvents. When the organic solvent evaporates, a thin film of this organic material remains on the dentin.
The disadvantages of the old cavity lining agents are that they are composed primarily of water-insoluble organic material which can only lay on top of a liquid layer that covers the surface of the dentin without any type of bond. This makes for a very leaky junction or union. The lack of adherence of the old cavity varnishes is such that they can wash out if the restoration leaks. If there is any gap or space between the restoration and the tooth, the lining varnish can move up or down depending on the direction of the forces of the leaking restoration.
The "smear layer" of microcrystalline debris, which is formed on the surface of all cut dentin, provides a natural cavity liner. It occludes the orifices of dentinal tubules to the point where bacteria cannot gain access to the tubules. Unfortunately, the particle size of the constituents making up the smear layer are so small that they have an enormous surface/volume ratio, making them extremely acid-labile. If there is any microleakage around the filling material and/or old-style cavity varnish, the smear layer is quickly dissolved.
The prior art includes U.S. Pat. No. 4,057,621 which discloses the use of oxalate salts to desensitize hypersensitive dentin or cementum sufaces teeth; and U.S. Pat. No. 2,746,905 which discloses the use of dehydroacetic acid and its water-soluble salts to maintain the pH of the mouth above 5.2 to prevent the dissolution of inorganic tooth enamel material and includes the use of oxalate in the composition as an enamel protective agent to increase the resistance of the tooth to acid attack.